PROJECT SUMMARY/ABSTRACT Cirrhosis of the liver can cause a spectrum of neurocognitive impairments known as hepatic encephalopathy (HE)1. HE ranges from minimal HE (MHE) all the way to overt HE (OHE) and coma, which can be life- threatening. It is very important to recognize and treat HE at its earliest stage of MHE before it escalates to more severe forms. If recognized early, MHE can be treated relatively easily with medications (e.g., lactulose, rifaximin) to avoid progression to OHE and other complications. Practice guidelines recommend frequent screening of all cirrhotic patients for MHE1. However, many studies demonstrate that cirrhotic patients are not getting adequately screened for MHE8, 9. This is likely because the current psychometric and neurophysiologic screening tests for MHE are complicated and time-consuming. They require specialized equipment and specially-trained personnel to administer. Critical flicker frequency (CFF) is the minimum frequency at which a flickering light source appears fused to an observer. MHE reduces CFF from 45-50Hz to <39 Hz7, 14-18. CFF is one of the best neurophysiologic tests for MHE. CFF has recently been shown to accurately detect MHE and to predict overall survival7. However, ascertainment of CFF currently requires specialized equipment, such as the Flicker Fusion System, which is not available in routine clinical practice, and is not designed to be self-administered at home due to its high cost, large size, and cumbersome operation. We developed a novel device for CFF testing called ?Flicker-App? designed to be small, portable, inexpensive and self-administered at home. The device consists of: (A) a light source that generates a flickering light at different frequencies from 25-55Hz, as controlled by communication via bluetooth with (B) a mobile app (Apple iOS) installed on an iPhone, which administers the protocol for determining CFF. Our goal is to perform a pilot and feasibility study to test the Flicker-App in 75 patients with cirrhosis, in order to: SA 1. Determine whether cirrhotic patients (n=75) can self-administer the Flicker-App in clinic supervised by a research assistant and calculate the level of agreement between the CFF determined by the Flicker-App, the CFF determined by the ?gold-standard? FFS device, and the test scores on the EncephalApp Stroop test. SA 2. Determine whether cirrhotic patients (n=75) can self-administer the Flicker-App at home, including daily measurements over 1 week and weekly measurements over 6 weeks, and calculate the adherence to this protocol and the variability of these CFF measurements. SA3. Make any necessary software or hardware adjustments to the Flicker-App to facilitate and simplify its self-administration by patients based on structured interview-questionnaires with the study participants and with clinical Gastroenterologists/Hepatologists.